68 



may be found of nearly the same girthing 

 for fifty or sixty feet in height. If the 

 yearhng shoot is one inch in diameter and 

 the two-year old shoot two inches in di- 

 ameter, the girthing of one will be double 

 that of the other; but if each shoot in- 

 creases annually one inch in diameter, the 

 proportion of their difference alters the 

 first year ; that is, the girthing of one, 

 instead of being twice as large, is only one 

 third larger than the other ; and when one 

 girths ten feet the other will girth ten feet 

 one inch, which is in effect no difference 

 at all. To grow valuable timber we should 

 not only aim at a maximum height of 

 branchless stem, but a maximum head on 

 a maximum height of branchless stem ; for 

 in proportion to the quantity of head will 

 be the quantity of its downward deposit, 

 or increase of the diameter of the stem. 



Against the theory of the one vernal 

 ascent and the one autumnal descent of 

 the sap, and in favour of the constant cir- 



